Air systems are known for the handling of air. In most air handling systems that involve comfort or environmental air handling a certain amount of outside or ambient air is mixed with recirculated inside air to produce an air quality desired for the associated facility. The requirement for such a system may be motivated by code requirements regarding occupancy levels, by varying the amount of outside air to compensate for the number of for example gas fork lift trucks operating in an enclosure, or to reduce the content of undesirable air contaminants. Such systems are normally equipped with modulating or single acting dampers the purpose of which is to provide a proper mix of outside air to return air. In such systems the outside damper is controlled along with an inside air damper to cause a mixed air result. Such an arrangement is common practice and is known to most practitioners.
The precise control of such a mixing, whether in accordance with a thermostat control for discharge air temperature or by any other sensor, is dependent on the precision of the dampers and the repeatability of an activating device and damper combination. Technical publications are available which are filled with technical advice on the proper method of designing dampers which begin to approach a linear action that will, for example, bring in 50% of outside or ambient air when an actuator moves by a magnitude of 50%. This leaves the control technology with the dilemma of creating a complex and costly control system subject to high maintenance costs to provide through non-linear dampers a specific amount of ambient air.
In the field with which the present invention is concerned, controlled make-up air systems, one has to match precisely the output of exhaust fans. The ability to signal the damper system and have it deliver a precise amount of air through the associated mixing dampers is extremely difficult with existing technology and particularly with the operational cycle of the dampers.